One method of joining two frame members is to cut the member end at 45.degree. to the longitudinal axis of the member, heat the extended ends of the member sheaths until they melt, and then to press the member ends together and to retain the member ends pressed together while the sheath ends cool and solidify to effect the joint.
With this known method the problem arises that the strength of the joint has to be provided by the relatively thin plastics sheaths.